Heating liquid in portable tanks

ABSTRACT

A heat exchanger apparatus for a portable tank that has an access opening and an access door removably attachable to seal the access opening. The apparatus includes a cover plate configured to be removably attached to the access opening to seal the access opening, and a heating circuit attached to an inner surface of the cover plate such that when the cover plate is attached to the access opening, the heating circuit extends into an interior of the tank. Input and output ports extend through the cover plate and are connected at inner ends thereof to the heating circuit such that fluid flowing into the input port flows through the heating circuit to the output port. The input and output ports are adapted at outer ends thereof for attachment to a fluid heating system to circulate heating fluid through the heating circuit.

This disclosure relates to the field of liquid heating equipment and inparticular equipment for heating liquid in portable tanks and likecontainers.

BACKGROUND

Heat exchangers are used in many industries for heating liquids, where ahot heating fluid, such as steam, water, glycol or the like, iscirculated through a heating circuit that is immersed in the targetliquid to be heated. Commonly the target liquid will be contained in atank or like container, and the heating circuit will be mounted insidethe tank with inlet and outlet ports exposed on the tank exterior. Afluid heating system, such as a boiler or water heater, or the like isconnected to the ports such that heating fluid enters the inlet port ata high temperature and flows through the heating circuit to the outletport where the temperature has dropped due to the transfer of heat tothe target liquid. The heating fluid then flows from the outlet portback to the fluid heating system where it is reheated.

The amount of heat transferred from the heating fluid to the targetfluid increases as the temperature difference (AT) between the hot fluidand the target liquid increases. Also the amount of heat removed fromthe heating fluid and transferred to the target liquid increases as thesurface area of the heating circuit that is exposed to the target liquidincreases, either by making the heating circuit longer, or by increasingthe surface area of the heating circuit per unit of length.

In many industries water is stored temporarily in large tanks that aretransported to and set up at a work location for various purposes. Oftenas well the stored water must be heated to a desired temperature. Onecommon large portable tank is the cylindrical 400 barrel (bbl) tank,with dimensions of about 12 feet in diameter and a height of about 20feet. These dimensions allow for fairly easy transport on roads on mostjurisdictions, and provide considerable capacity of 400 bbl or 16,800 USgallons. Oil well fracturing operations for example may utilize several400 bbl or similar large capacity tanks as these operations requirelarge quantities of water, and commonly also require that the water beheated to temperatures up to 140° F.

Conventional large tanks have access doors that provide access throughan access opening to the tank interior for personnel to enter and cleanthe tank interior. The dimensions of the access openings are fairlystandard for any given size of tank. As well, to facilitate heating thewater in the tank, a heating circuit is sometimes mounted inside thetank. The conventional mounted heating circuit typically comprises a twoinch diameter steel pipe supported inside the tank somewhat above thetank floor and following inside the cylindrical wall from a first portextending through the tank wall to a second port extending through thetank wall. A heating system is connected to the ports and hot heatingfluid is circulated through the pipe to warm the target liquid, beingthe water in the tank. The total length of the heating circuit issomewhat less than π times the tank diameter (Da), and so for a 12 footdiameter tank, the length will be about 30 feet.

With the small outer surface area provided by 30 feet of two inch pipe,in order to transfer sufficient heat to raise the temperature of thewater, the heating fluid must be quite high, increasing the AT betweenthe heating and target fluids and increasing the heat transfer rate.Thus where high temperature water is required, it is common to use steamas the heating fluid, since the steam temperature can be maintained atabout 300° F.

The use of steam heating systems however has significant drawbacks. Thesteam pressure can easily exceed 2000 pounds per square inch (psi) soeven a small leak can cause serious injury to nearby personnel. Steamheaters are considered high pressure vessels, since they are closed tothe atmosphere, and as such require operators with specialized trainingin the operation of the steam system. To handle the high pressures, thepipe of the conventional permanently mounted heating circuit is quitethick, and there can thus be a significant temperature gradient betweenthe inside and outside surface of the wall, such that heat does nottransfer as readily as it would though a thin wall pipe where thetemperature gradient between the inside and outside surfaces of the wallis less.

A further problem with steam is that steam condenses back into water inthe steam loop, and so vessels or conduits can be ruptured whentemperatures reach below freezing and trapped water expands.

Alternatively, a glycol heating system can be used where a hot glycolliquid is circulated through the pipe. While other liquids can be used,glycol is a popular choice as it is not subject to freezing and thedamage that can result from same. These glycol systems are open to theatmosphere and so pressures in the heating circuit are only thoserequired to circulate the glycol, about 20-40 psi. There are no highpressures or danger of explosion, and so specially qualified personnelare not required. The temperature of the glycol must be kept below theboiling point, or at a maximum of about 200° F. The rate of heattransfer is therefore much less than when using a steam heating systemat 300° F., and the glycol heating systems are thus mainly used toprevent the water in the tank from freezing.

It is also known to draw water from the tank and pass the water througha water heater and return the water back to the tank. A problem in manysituations is that the water in the tank is often contaminated andspillage can cause environmental damage and costly clean-up operations.Drawing the contaminated water out of the tank exposes same to the riskof freezing and subsequent rupture of lines and spillage if equipmentfails. Seals and the like are also subject to failure and subsequentcontaminated leakage.

These portable tanks are subjected to considerable shock forces whenlifted and tipped horizontally onto a vehicle deck for transport. Duringtransport to the work site as well, these tanks are often carried overrough roads and so the heating circuit must be robust to avoid damage.The thick wall pipe thus also serves to resist damage, although damagecan occur at the ports through the tank wall, or to the support legsholding the pipe above the tank floor, as the pipe flexes and vibratesduring transit over rough roads.

SUMMARY OF THE INVENTION

The present disclosure provides a heat exchanger apparatus thatovercomes problems in the prior art.

In a first embodiment the present disclosure provides a heat exchangerapparatus for a portable tank, where the portable tank includes anaccess opening and an access door removably attachable to seal theaccess opening. The apparatus comprises a cover plate configured to beremovably attached to the access opening to seal the access opening, anda heating circuit attached to an inner surface of the cover plate suchthat when the cover plate is attached to the access opening, the heatingcircuit extends into an interior of the tank. Input and output portsextend through the cover plate and are connected at inner ends thereofto the heating circuit such that fluid flowing into the input port flowsthrough the heating circuit to the output port. The input and outputports are adapted at outer ends thereof for attachment to a fluidheating system to circulate heating fluid through the heating circuit.

In a second embodiment the present disclosure provides a method ofheating a target liquid in a portable tank, where the portable tankincludes an access opening and an access door removably attachable toseal the access opening. The method comprises configuring a cover plateto be removably attached to the access opening to seal the accessopening; attaching a heating circuit to an inner surface of the coverplate such that when the cover plate is attached to the access opening,the heating circuit extends into an interior of the tank; extendinginput and output ports through the cover plate and connecting inner endsthereof to the heating circuit; installing the tank at a desiredlocation; attaching the cover plate to the access opening such that theheating circuit extends into the interior of the tank, and such that theaccess opening is sealed; filling the tank with the target liquid to alevel above the heating circuit; attaching outer ends of the input andoutput ports to a fluid heating system and circulating heating fluidthrough the heating circuit.

The present disclosure provides a heat exchanger apparatus for aportable tank that provides sufficient surface area to allow glycol at200° F. to heat the target liquid, thus avoiding the complicationsencountered when using pressurized steam at 300° F. The target liquid isalso kept inside the tank at all times, reducing the risk of spillage.

The risk of damage to the heat exchanger apparatus during loading andtransport of the tank is reduced as the heat exchanger apparatus cansimply be removed and transported separately. As well the portable tanksof the kind contemplated for use with the presently disclosed apparatusand method are fairly standard in construction and instead of installinga permanent heat exchanger apparatus in tanks which might possibly beused for heating liquid, the heat exchanger apparatus of the presentdisclosure can be simply installed in any tank where heat is required.Thus the present disclosure provides considerable versatility andreduces costs.

DESCRIPTION OF THE DRAWINGS

While the invention is claimed in the concluding portions hereof,preferred embodiments are provided in the accompanying detaileddescription which may be best understood in conjunction with theaccompanying diagrams where like parts in each of the several diagramsare labeled with like numbers, and where:

FIG. 1 is a schematic front view of a portable tank of the prior artwith the access door removed;

FIG. 2 is a schematic top view of an embodiment of the heat exchangerapparatus of the present disclosure;

FIG. 3 is a schematic front view of the embodiment of FIG. 2;

FIG. 4 is a schematic side view of the embodiment of FIG. 2;

FIG. 5 is a schematic side view of a heat exchanger apparatus of thepresent disclosure installed in the portable tank of FIG. 1;

FIG. 6 is a schematic side view of a heat exchanger apparatus of thepresent disclosure in the process of being installed in the portabletank of FIG. 1;

FIG. 7 is a schematic sectional view of a heating conduit for use in theembodiment of FIG. 2;

FIG. 8 is a schematic side view of the tank of FIG. 1 loaded on a firstvehicle for transport, and the heat exchanger apparatus of FIG. 2 loadedon a second vehicle for transport.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 illustrates common portable tank 1 of the prior art of the typewhich includes an access opening 3 and an access door 5 that isremovably attachable to seal the access opening 3. In the illustratedtank 1 the opening 3 is surrounded by a flange 7, and the door 5 isattached with bolts through corresponding holes 9 in the flange 7 anddoor 5, and a gasket, sealant, or the like is typically placed betweenthe flange and the door 5 to provide a seal.

FIGS. 2-4 schematically illustrate an embodiment of a heat exchangerapparatus 10 of the present disclosure for use with the portable tank 1.The apparatus 10 comprises a cover plate 11 configured to be removablyattached to the access opening 3 to seal the access opening in the samemanner as the door 5 described above. The cover plate 11 also definesholes 9 that correspond to the holes in the flange 7 surrounding theaccess opening 3.

A heating circuit 13 is attached to the inner surface 11A of the coverplate 11 such that when the cover plate 11 is attached to the accessopening 3, the heating circuit 13 extends into an interior of the tank 1as schematically illustrated in FIG. 5.

Input and output ports 15A, 15B extend through the cover plate 11 andconnect at inner ends 17 thereof to the heating circuit 13 such thatfluid flowing into the input port 15A flows through the heating circuit13 to the output port 15B. The input and output ports 15A, 15B areadapted at outer ends 19 thereof for attachment to a fluid heatingsystem 21 to circulate heating fluid through the heating circuit 13. Thefluid heating system 21 can use steam, glycol, water, as the heatingfluid. The present apparatus 10 provides a large surface area for heattransfer from the heating fluid to the target liquid such that anun-pressurized glycol or water fluid heating system 21 can effectivelyheat the target fluid, and it is contemplated that typically the userwill prefer such an un-pressurized system to avoid the hazards andspecialized personnel requirements of a steam system.

In the illustrated apparatus 10, the heating circuit 13 comprises aheating conduit 23 extending from the inner surface 11A of the coverplate 11 towards a far wall 25 of the tank 1 opposite the access opening3, as schematically illustrated in FIG. 5. In the illustrated apparatus10, the heating circuit 13 comprises a plurality of loops of heatingconduit 23 extending back and forth between the far wall 25 and thecover plate 11. The added length of the heating circuit 13 provided bylooping the heating conduit 23 back and forth increases the surface areaexposed to the target liquid in the tank 1 and thereby increases theamount of heat transferred from the heating fluid in the heating circuit13 to the target fluid in the tank 1.

The illustrated heating conduit 23 is also provided by corrugatedtubing, as schematically illustrated in FIG. 7. The corrugations 27further increase the surface area exposed to the target liquid in thetank 1, and also ensure turbulent flow rather than laminar flow insidethe heating conduit 23, which turbulent flow ensures that the fluid ismixed and at a substantially uniform temperature across the diameter ofthe conduit 23.

The corrugated heating conduit 23 is also flexible, which providesversatility in making up the heating circuit 13. The heating conduit 23is conveniently provided by corrugated stainless steel tubing with awall thickness T that is less than about 0.015 inches. Such tubing isreadily available as the inner stainless steel portion of a flexible gasline is provided by such tubing with a wall thickness T of 0.010 inches,which is then covered by a coating for use as a gas line. When used asthe heating conduit 23 in the present disclosure, the stainless steeltubing with the very thin wall is an excellent conductor, allowing heatto pass readily from the heating fluid flowing in the heating conduitthrough the tubing wall to the target fluid, and is also very light,facilitating manipulation of the apparatus 10 during installation.

To add structure to the heating circuit 13, especially where the heatingconduit 23 is flexible but also where a rigid heating conduit 23 isused, a brace member 29 is attached to the inner surface 11A of thecover plate 11 and extends toward the far wall along the heating circuit13, and the heating conduit 23 is supported on the brace member 29 asschematically illustrated in FIGS. 2 and 4.

To facilitate manual manipulation of the apparatus 10, the brace member29 should be as light weight as possible, and can be, for example, anopen framework made with aluminum tubing. Other brace structure could beused as well. To minimize weight, the cover plate 11 can also be madefrom aluminum, or some other light weight material. Some plastics may besuitable, as the pressure against the cover plate 11 is typically notexcessive.

Also in the illustrated apparatus 10, a support member 31, is mounted ona bottom inner portion of the heating circuit 13. The support member 31is typically a skid adapted to slide along the tank floor 33 and supportthe inside end of the heating circuit 13 as it moves into the interiorof the tank 1 during installation of the cover plate 11, asschematically illustrated in FIG. 6. The support member 31 can bemounted on the brace member 29 as seen in FIG. 4, or directly on theheating circuit 13 when a rigid heating conduit is used and there is nosupport member required.

The present disclosure provides a method of heating a target liquid in aportable tank 1, where the portable tank 1 includes an access opening 3and an access door 5 removably attachable to seal the access opening.The method comprises configuring a cover plate 11 to be removablyattached to the access opening 3 to seal the access opening; attaching aheating circuit 13 to an inner surface 11A of the cover plate 11 suchthat when the cover plate is attached to the access opening 3, theheating circuit 13 extends into an interior of the tank 1; extendinginput and output ports 15 through the cover plate 11 and connectinginner ends 17 thereof to the heating circuit 13; installing the tank 1at a desired location; attaching the cover plate 11 to the accessopening 3 such that the heating circuit 13 extends into the interior ofthe tank 1, and such that the access opening 3 is sealed; filling thetank 1 with the target liquid to a level above the heating circuit 13;attaching outer ends 19 of the input and output ports 15 to a fluidheating system 21 and circulating heating fluid through the heatingcircuit 13.

When it is desired to move the tank 1 to a different location, thetarget liquid is removed from the tank 1 and the cover plate 11 isremoved from the access opening 3 the heating circuit 13 is withdrawnfrom the interior of the tank; loading the tank 1 and the heat exchangerapparatus 10 comprising the cover plate 11 with heating circuit 13 onone or more vehicles for transport. FIG. 8 schematically illustrates thetank 1 loaded on a first vehicle 35 and the heat exchanger apparatus 10loaded on a second vehicle 37. Removing the heat exchanger apparatus 10from the tank prior to loading the tank 1 on the vehicle 35 avoidssubjecting the apparatus 10 to shock forces when the tank 1 is tippedonto the vehicle 35. Transporting the apparatus 10 separately alsoallows for cradling the apparatus 10 on the vehicle 37 to avoid damageduring transport on the rough roads often encountered. Also the heatexchanger apparatus 10 and the tank 1 may well be going to differentlocations.

The present disclosure provides a heat exchanger apparatus 10 for aportable tank 1 that provides sufficient surface area to allow glycol at200° F. to heat the target liquid, thus avoiding the complicationsencountered when using pressurized steam at 300° F. The target liquid isalso kept inside the tank 1 at all times, reducing the risk of spillage.

Portable tanks of the kind contemplated for use with the presentlydisclosed apparatus and method are fairly standard in construction andthe heat exchanger apparatus 10 can be configured to be installed onsuch a tank, and then used on any other tank with the same accessopening, providing considerable versatility. The expense of installing apermanent heat exchanger system in each tank is avoided.

The foregoing is considered as illustrative only of the principles ofthe invention. Further, since numerous changes and modifications willreadily occur to those skilled in the art, it is not desired to limitthe invention to the exact construction and operation shown anddescribed, and accordingly, all such suitable changes or modificationsin structure or operation which may be resorted to are intended to fallwithin the scope of the claimed invention.

What is claimed is:
 1. A heat exchanger apparatus for a portable tank,where the portable tank includes an access opening and an access doorremovably attachable to seal the access opening, the apparatuscomprising: a cover plate configured to be removably attached to theaccess opening to seal the access opening; a heating circuit attached toan inner surface of the cover plate such that when the cover plate isattached to the access opening, the heating circuit extends into aninterior of the tank; input and output ports extending through the coverplate and connected at inner ends thereof to the heating circuit suchthat fluid flowing into the input port flows through the heating circuitto the output port; the input and output ports adapted at outer endsthereof for attachment to a fluid heating system to circulate heatingfluid through the heating circuit.
 2. The apparatus of claim 1 whereinthe heating circuit comprises a heating conduit extending from the innersurface of the cover plate towards a far wall of the tank opposite theaccess opening.
 3. The apparatus of claim 2 wherein the heating circuitcomprises a plurality of loops of heating conduit extending back andforth between the far wall and the cover plate.
 4. The apparatus ofclaim 3 wherein the heating conduit is provided by corrugated tubing. 5.The apparatus of claim 4 wherein the heating conduit is flexible, andcomprising a brace member attached to the inner surface of the coverplate and extending toward the far wall, and wherein the heating conduitis supported on the brace member.
 6. The apparatus of claim 5 comprisinga support member mounted on a bottom inner portion of the brace memberand adapted to move along a tank floor as the heating circuit moves intothe interior of the tank during installation of the cover plate.
 7. Theapparatus of claim 5 wherein the brace member is made from aluminum. 8.The apparatus of claim 5 wherein the heating conduit is provided bycorrugated stainless steel tubing with a wall thickness less than about0.015 inches.
 9. The apparatus of claim 7 wherein the heating conduit isprovided a stainless steel portion of a flexible gas line, where theflexible gas line comprises the stainless steel portion covered by acoating.
 10. The apparatus of claim 4 wherein the heating conduit issubstantially rigid.
 11. The apparatus of claim 10 comprising a supportmember mounted on a bottom inner portion of the rigid heating conduitand configured to move along a tank floor as the heating circuit movesinto the interior of the tank during installation of the cover plate.12. The apparatus of claim 1 wherein the cover plate is made fromaluminum.
 13. A method of heating a target liquid in a portable tank,where the portable tank includes an access opening and an access doorremovably attachable to seal the access opening, the method comprising:configuring a cover plate to be removably attached to the access openingto seal the access opening; attaching a heating circuit to an innersurface of the cover plate such that when the cover plate is attached tothe access opening, the heating circuit extends into an interior of thetank; extending input and output ports through the cover plate andconnecting inner ends thereof to the heating circuit; installing thetank at a desired location; attaching the cover plate to the accessopening such that the heating circuit extends into the interior of thetank, and such that the access opening is sealed; filling the tank withthe target liquid to a level above the heating circuit; attaching outerends of the input and output ports to a fluid heating system andcirculating heating fluid through the heating circuit.
 14. The method ofclaim 13 comprising, when it is desired to move the tank to a differentlocation, removing the target liquid from the tank; removing the coverplate from the access opening and removing the heating circuit from theinterior of the tank; loading the tank and the cover plate with theheating circuit on one or more vehicles for transport.
 15. The method ofclaim 13 wherein the heating circuit comprises a heating conduitextending from the inner surface of the cover plate towards a far wallof the tank opposite the access opening.
 16. The method of claim 15wherein the heating circuit comprises a plurality of loops of heatingconduit extending back and forth between the far wall and the coverplate.
 17. The method of claim 16 wherein the heating conduit isprovided by corrugated tubing.
 18. The method of claim 17 wherein theheating conduit is flexible, and comprising a brace member attached tothe inner surface of the cover plate and extending toward the far wall,and wherein the heating conduit is supported on the brace member. 19.The method of claim 18 comprising mounting a support member on a bottominner portion of the brace member and resting the support member on atank floor as the heating circuit moves into the interior of the tankduring installation of the cover plate.
 20. The method of claim 16wherein the heating conduit is substantially rigid.